1. Field of the Invention
The present invention relates generally to structural components, and, specifically, to armors. In particular, the present invention relates to armors including a material that is capable of undergoing at least one of a reversible phase change and/or an elastic strain deformation of at least 5% when an object impacts the armors and transfers sufficient energy to the armors. The present invention is also directed to methods of manufacturing such armors. The armors of the invention find application as, for example, a protective facing material for armored vehicles, such as tanks, helicopters, trucks, and the like.
2. Description of the Invention Background
Historically, armored combat vehicles were protected by heavy metallic armors made from, for example, iron or high alloy steels. As more powerful and sophisticated armor piercing projectiles were developed, armors made from these conventional materials had to be made more resistant to penetration. This was generally achieved by making the armor thicker, which had the disadvantage of making the armor heavier.
In response to the development of sophisticated armor piercing rounds, stronger but lighter materials began to be used. For example, Ti-6Al-4V (nominally 6 weight percent aluminum, 4 weight percent vanadium, balance essentially titanium) has good penetration resistance and, therefore, has become a widely used armor material. This alloy, which is relatively lightweight, absorbs the energy of a projectile by spreading the energy out across its mass, thereby blunting the tip of the projectile and resisting penetration. Military Specification MIL-A-40677 sets forth the military requirements for such armors. Various modifications to the composition of titanium-based armors have been proposed, some of which are taught in U.S. Pat. Nos. 6,053,993, 5,980,655, and 5,332,545.
Recently, conventional lightweight armors, including titanium-base armors, have been thwarted by advanced armor piercing rounds designed to concentrate their energy within a very small area that may melt the armor material. In response, ceramic-based armors have been developed. Ceramics are used in the fabrication of armors because they are lightweight and extremely hard materials. One of the drawbacks with ceramic armors, however, is that they dissipate the energy of the projectile partially by cracking. Therefore, ceramic armors lack repeat hit capability, i.e., they will not resist penetration if hit in the same position multiple times, and they disintegrate if struck by multiple rounds. Attempts have been made to address this problem, one of which is disclosed in U.S. Pat. No. 4,987,033, which teaches an armor that uses a Ti-6Al-4V layer surrounding a ceramic-based core. Nevertheless, while this design provides somewhat improved performance, the ceramic core eventually cracks when struck multiple times, thereby eliminating the armor's effectiveness. Moreover, the cost of ceramic armors may be exorbitant.
Another class of armor design is the so-called reactive armor. Here, the armor includes an explosive material that, when contacted by the projectile, explodes violently. In this design, the outward force of the reactive armor explosion counteracts the force of the incoming projectile, thereby resisting penetration of the armor. Reactive armor designs may also include movable members that may, for example, absorb the energy of the projectile, blunt the projectile, modify the trajectory of the projectile, and/or destroy the projectile. An example of such an armor design is disclosed in U.S. Pat. No. 5,293,806. Reactive armors, however, like ceramic armors, are deficient in that they do not have multi-shot capability, i.e., they do not provide substantial protection against multiple hits occurring in the same region. Once the reactive armor is activated, a second round hitting the armor in the same location is much more likely to penetrate the armor.
Thus, it is desirable to provide a lightweight armor having multi-shot capability that is able to withstand the energy of advanced armor piercing rounds.